Identification of a Membrane Protein, LAT-2, That Co-expresses with 4F2 Heavy Chain, an L-type Amino Acid Transport Activity with Broad Specificity for Small and Large Zwitterionic Amino Acids

Two different protein families, designated CAT (cationic amino acid transporter) and BAT (broad-specificity amino acid transporter) mediate the plasma membrane transport of cationic amino acids in animal cells. CAT transporters have 12-14 transmembrane domains and are selective for cationic amino acids. BAT proteins, in contrast, have one to four transmembrane domains and induce the transport of both cationic and zwitterionic amino acids when expressed in Xenopus oocytes. Mutations in the human BAT gene cause type I cystinuria, a disease affecting the ability of intestinal and renal brush border membranes to transport cationic amino acids and cystine. We have used functional expression cloning in oocytes to isolate a BAT-related cDNA from rat jejunal epithelium. The cDNA encodes the rat 4F2 heavy chain (4F2hc) cell-surface antigen, a 527-residue (60 kDa) protein that is 26% identical in amino acid sequence with rat renal BAT (also known as NBAT/D2). Expression of rat jejunal 4F2hc in oocytes induced the lysine-inhibitable Na+-dependent influx of leucine and the leucine-inhibitable Na+-independent influx of lysine. Lysine efflux was stimulated by extracellular (Na+ plus leucine). These characteristics identify the expressed amino acid transport activity as system y+L, a transporter that has been implicated in basal membrane transport of cationic amino acids in intestine, kidney and placenta.

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Alkali Cations, Freeze-thawing and Reconstitution of Na+-Dependent Amino-Acid Transport Activity

Annals of the New York Academy of Sciences ◽

10.1111/j.1749-6632.1985.tb14855.x ◽

1985 ◽

Vol 456 (1 Membrane Tran) ◽

pp. 121-123

Author(s):

JOHN I. MCCORMICK ◽

ROSE M. JOHNSTONE

Keyword(s):

Amino Acid ◽

Amino Acid Transport ◽

Acid Transport ◽

Transport Activity ◽

Alkali Cations

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Amino acid transport in normal and glutathione-deficient sheep erythrocytes

Biochemical Journal ◽

10.1042/bj1540043 ◽

1976 ◽

Vol 154 (1) ◽

pp. 43-48 ◽

Cited By ~ 53

Author(s):

J D Young ◽

J C Ellory ◽

E M Tucker

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Amino Acid Transport ◽

Cell Types ◽

The Other ◽

Acid Transport ◽

Sheep Erythrocytes ◽

Uptake Rates

1. Uptake rates for 23 amino acids were measured for both normal (high-GSH) and GSH-deficient (low-GSH) erythrocytes from Finnish Landrace sheep. 2. Compared with high-GSH cells, low-GSH cells had a markedly diminished permeability to D-alanine, L-alanine, α-amino-n-butyrate, valine, cysteine, serine, threonine, asparagine, lysine and ornithine. Smaller differences were observed for glycine and proline, whereas uptake of the other amino acids was not significantly different in the two cell types.

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Amino Acid Transport in a Water-mould: The Possible Regulatory Roles of Calcium and N6-(Δ2-isopentenyl)adenine

Canadian Journal of Biochemistry ◽

10.1139/o75-134 ◽

1975 ◽

Vol 53 (9) ◽

pp. 975-988 ◽

Cited By ~ 7

Author(s):

Danny P. Singh ◽

Hérb. B. LéJohn

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Amino Acid Transport ◽

Osmotic Shock ◽

Inhibitory Effect ◽

Transport Systems ◽

Acid Transport ◽

Isopentenyl Adenine ◽

Energy Dependent ◽

Water Mould

Transport of amino acids in the water-mould Achlya is an energy-dependent process. Based on competition kinetics and studies involving the influence of pH and temperature on the initial transport rates, it was concluded that the 20 amino acids (L-isomers) commonly found in proteins were transported by more than one, possibly nine, uptake systems. This is similar to the pattern elucidated for some bacteria but unlike those uncovered for all fungi studied to date. The nine different transport systems elucidated are: (i) methionine, (ii) cysteine, (iii) proline, (iv) serine–threonine, (v) aspartic and glutamic acids, (vi) glutamine and asparagine, (vii) glycine and alanine, (viii) histidine, lysine, and arginine, and (ix) phenylalanine–tyrosine–tryptophan and leucine–isoleucine–valine as two overlapping groups. Transport of all of these amino acids was inhibited by azide, cyanide, and its derivatives and 2,4-dinitrophenol. These agents normally interfere with metabolism at the level of the electron transport chain and oxidative phosphorylation. Osmotic shock treatment of the cells released, into the shock fluid, a glycopeptide that binds calcium as well as tryptophan but no other amino acid. The shocked cells are incapable of concentrating amino acids, but remain viable and reacquire this capacity when the glycopeptide is resynthesized.Calcium played more than a secondary role in the transport of the amino acids. When bound to the membrane-localized glycopeptide, it permits concentrative transport to take place. However, excess calcium can inhibit transport which can be overcome by chelating with citrate. Calculations show that the concentration of free citrate is most important. At low citrate concentrations (less than 1 mM) in the absence of exogenously supplied calcium, enhancement of amino acid transport occurs. At high concentrations (greater than 5 mM), citrate inhibits but this effect can be reversed by titrating with calcium. Evidently, the glycopeptide acts as a calcium sink to regulate the concentration of calcium made available to the cell for its membrane activities.N6-(Δ2-isopentenyl) adenine (a plant growth 'hormone') and analogues mimic the inhibitory effect of citrate and bind to the glycopeptide as well. Replot data for citrate and N6-(Δ2-isopentyl) adenine inhibition indicate that both agents have no more than one binding constant. These results implicate calcium, glycopeptide, and energy-dependent transport of solutes in some, as yet undefinable, way.

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Placental amino acid transport

AJP Cell Physiology ◽

10.1152/ajpcell.1995.268.6.c1321 ◽

1995 ◽

Vol 268 (6) ◽

pp. C1321-C1331 ◽

Cited By ~ 85

Author(s):

A. J. Moe

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Human Placenta ◽

Amino Acid Transport ◽

Single Layer ◽

Maternal Blood ◽

Transport Systems ◽

Amino Acid Transporters ◽

Acid Transport ◽

Principal Mechanism

Normal fetal growth and development depend on a continuous supply of amino acids from the mother to the fetus. The placenta is responsible for the transfer of amino acids between the two circulations. The human placenta is hemomonochorial, meaning that the maternal and fetal circulations are separated by a single layer of polarized epithelium called the syncytiotrophoblast, which is in direct contact with maternal blood. Transport proteins located in the microvillous and basal membranes of the syncytiotrophoblast are the principal mechanism for transfer from maternal blood to fetal blood. Knowledge of the function and regulation of syncytiotrophoblast amino acid transporters is of great importance in understanding the mechanism of placental transport and potentially improving fetal and newborn outcomes. The development of methods for the isolation of microvillous and basal membrane vesicles from human placenta over the past two decades has contributed greatly to this understanding. Now a primary cultured trophoblast model is available to study amino acid transport and regulation as the cells differentiate. The types of amino acid transporters and their distribution between the syncytiotrophoblast microvillous and basal membranes are somewhat unique compared with other polarized epithelia. These differences may reflect the unusual circumstance of this epithelium that is exposed to blood on both sides. The current state of knowledge as to the types of transport systems present in syncytiotrophoblast, their regulation, and the effects of maternal consumption of drugs on transport are discussed.

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Multiple pathways for cationic amino acid transport in rat thyroid epithelial cell line PC Cl3

AJP Cell Physiology ◽

10.1152/ajpcell.00053.2004 ◽

2005 ◽

Vol 288 (2) ◽

pp. C290-C303 ◽

Cited By ~ 10

Author(s):

Tiziano Verri ◽

Cinzia Dimitri ◽

Sonia Treglia ◽

Fabio Storelli ◽

Stefania De Micheli ◽

...

Keyword(s):

Amino Acids ◽

Amino Acid ◽

Cell Line ◽

Amino Acid Transport ◽

Transport Systems ◽

Residual Fraction ◽

Acid Transport ◽

Thyroid Cells ◽

Cationic Amino Acid ◽

Rat Thyroid

Information regarding cationic amino acid transport systems in thyroid is limited to Northern blot detection of y+LAT1 mRNA in the mouse. This study investigated cationic amino acid transport in PC cell line clone 3 (PC Cl3 cells), a thyroid follicular cell line derived from a normal Fisher rat retaining many features of normal differentiated follicular thyroid cells. We provide evidence that in PC Cl3 cells plasmalemmal transport of cationic amino acids is Na+ independent and occurs, besides diffusion, with the contribution of high-affinity, carrier-mediated processes. Carrier-mediated transport is via y+, y+L, and b0,+ systems, as assessed by l-arginine uptake and kinetics, inhibition of l-arginine transport by N-ethylmaleimide and neutral amino acids, and l-cystine transport studies. y+L and y+ systems account for the highest transport rate (with y+L > y+) and b0,+ for a residual fraction of the transport. Uptake data correlate to expression of the genes encoding for CAT-1, CAT-2B, 4F2hc, y+LAT1, y+LAT2, rBAT, and b0,+AT, an expression profile that is also shown by the rat thyroid gland. In PC Cl3 cells cationic amino acid uptake is under TSH and/or cAMP control (with transport increasing with increasing TSH concentration), and upregulation of CAT-1, CAT-2B, 4F2hc/y+LAT1, and rBAT/b0,+AT occurs at the mRNA level under TSH stimulation. Our results provide the first description of an expression pattern of cationic amino acid transport systems in thyroid cells. Furthermore, we provide evidence that extracellular l-arginine is a crucial requirement for normal PC Cl3 cell growth and that long-term l-arginine deprivation negatively influences CAT-2B expression, as it correlates to reduction of CAT-2B mRNA levels.

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Expression of solute carrier 7A4 (SLC7A4) in the plasma membrane is not sufficient to mediate amino acid transport activity

Biochemical Journal ◽

10.1042/bj20020084 ◽

2002 ◽

Vol 364 (3) ◽

pp. 767-775 ◽

Cited By ~ 40

Author(s):

Sabine WOLF ◽

Annette JANZEN ◽

Nicole VÉKONY ◽

Ursula MARTINÉ ◽

Dennis STRAND ◽

...

Keyword(s):

Plasma Membrane ◽

Amino Acid ◽

Protein Expression ◽

Amino Acid Transport ◽

Fluorescent Protein ◽

Xenopus Laevis Oocytes ◽

Amino Acid Transporters ◽

Acid Transport ◽

Transport Activity ◽

Solute Carrier

Member 4 of human solute carrier family 7 (SLC7A4) exhibits significant sequence homology with the SLC7 subfamily of human cationic amino acid transporters (hCATs) [Sperandeo, Borsani, Incerti, Zollo, Rossi, Zuffardi, Castaldo, Taglialatela, Andria and Sebastio (1998) Genomics 49, 230–236]. It is therefore often referred to as hCAT-4 even though no convincing transport activity has been shown for this protein. We expressed SLC7A4 in Xenopus laevis oocytes, but could not detect any transport activity for cationic, neutral or anionic amino acids or for the polyamine putrescine. In addition, human glioblastoma cells stably overexpressing a fusion protein between SLC7A4 and the enhanced green fluorescent protein (EGFP) did not exhibit an increased transport activity for l-arginine. The lack of transport activity was not due to a lack of SLC7A4 protein expression in the plasma membrane, as in both cell types SLC7A4-EGFP exhibited a similar subcellular localization and level of protein expression as functional hCAT-EGFP proteins. The expression of SLC7A4 can be induced in NT2 teratocarcinoma cells by treatment with retinoic acid. However, also for this endogenously expressed SLC7A4, we could not detect any transport activity for l-arginine. Our data demonstrate that the expression of SLC7A4 in the plasma membrane is not sufficient to induce an amino acid transport activity in X. laevis oocytes or human cells. Therefore, SLC7A4 is either not an amino acid transporter or it needs additional (protein) factor(s) to be functional.

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